HANDBOOK OF PHYSIOLOGY. 



respiratory undulations. The action of this centre in producing such 

 undulations is thus demonstrated. In an animal under the influence 

 of urari, a record of whose blood-pressure is being taken, and where 

 artificial respiration has been stopped, and both vagi cut, the blood- 

 pressure curve rises at first almost in a straight line, but after a time 

 rhythmical undulations occur (called Traube's or Traube- Her ing's 

 curves) ; there may be upward of ten of the respiratory undulations in 

 one Traube-Hering curve. They continue as long as the blood-pressure 

 continues to rise, and only cease when the vaso-motor centie and the 

 heart are exhausted, when the pressure falls. The undulations cannot 

 depend upon anything but the vaso-motor centre, as the mechanical 

 effects of respiration have been eliminated by the urari and by the 

 cessation of artificial respiration, . J ,nd the effect of the cardio-inhibitory 

 centre has been removed, by the division of the vagi. The rhythmic 

 rise of blood-pressure is most likely due to a rhythmic constriction of 

 the arterioles followed by a rhythmic fall of pressure and relaxation, 

 both being due to the action of the vaso-motor centre. The vaso-motor 

 centre, therefore, as well as the cardio-inhibitory, is capable of produc- 

 ing rhythmical undulations of blood-pressure. 



Chcync-Stokcs' breathing is a rhythmical irregularity in respirations 

 which has been observed in various diseases, and is especially connected 

 with fatty degeneration of the heart. Respirations occur in groups, at 

 the beginning of each group the inspirations are very shallow, but each 

 successive breath is deeper than the preceding, until a climax is reached, 

 after which the inspirations become less and less deep, until they cease 

 after a slight pause altogether. This phenomenon appears to be due to 

 the want of action of some of the usual cerebral influences which pass 

 down to and regulate the discharges of the respiratory centres. 



Whatever is the exact quality of the venous blood which excites the 

 respiratory centre to produce normal respirations, there can be no doubt 

 that as the blood becomes more and more venous from obstruction to 

 the entrance of air into the lung, or from the blood not taking up from 

 the air its usual supply of oxygen, the respiratory centre becomes more 

 active and excitable, and a condition ensues, which passes rapidly from 

 Hypcrpnwa (excessive breathing) to the state of Dyspnoea (difficult 

 breathing), and afterward to Asphyxia ; and' the latter, unless relieved, 

 quickly ends in death. 



The ways by which this condition of asphyxia may be produced are 

 very numerous: As, for example, by the prevention of the due entry 

 of oxygen into the blood, either by direct obstruction of the trachea or 

 other part of the respiratory passages, or by introducing instead of 

 ordinary air a gas devoid of oxygen, or, by interference with the due in- 

 terchange of gases between the air and the blood. 



The symptoms of asphyxia may be divided into three groups, which 



